President Donald Trump's zeal for new a round of tariffs is running into cold, hard economic and political reality: lawmakers from his own party who think it's a bad idea.

Twice this week Trump has raised the idea of trade penalties he calls a "reciprocal tax," only to have White House officials insist there's no plan in the works for such an action. During a televised meeting at the White House on Tuesday, Republican lawmakers told Trump the new tariffs he's mulling for aluminum and steel...